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    <pre><code>string s = (string)o; // 1 </code></pre> <p>Throws <a href="https://msdn.microsoft.com/en-us/library/system.invalidcastexception" rel="noreferrer">InvalidCastException</a> if <code>o</code> is not a <code>string</code>. Otherwise, assigns <code>o</code> to <code>s</code>, even if <code>o</code> is <code>null</code>.</p> <pre><code>string s = o as string; // 2 </code></pre> <p>Assigns <code>null</code> to <code>s</code> if <code>o</code> is not a <code>string</code> or if <code>o</code> is <code>null</code>. For this reason, you cannot use it with value types (the operator could never return <code>null</code> in that case). Otherwise, assigns <code>o</code> to <code>s</code>.</p> <pre><code>string s = o.ToString(); // 3 </code></pre> <p>Causes a <a href="https://msdn.microsoft.com/en-us/library/system.nullreferenceexception" rel="noreferrer">NullReferenceException</a> if <code>o</code> is <code>null</code>. Assigns whatever <code>o.ToString()</code> returns to <code>s</code>, no matter what type <code>o</code> is.</p> <hr> <p>Use 1 for most conversions - it's simple and straightforward. I tend to almost never use 2 since if something is not the right type, I usually expect an exception to occur. I have only seen a need for this return-null type of functionality with badly designed libraries which use error codes (e.g. return null = error, instead of using exceptions).</p> <p>3 is not a cast and is just a method invocation. Use it for when you need the string representation of a non-string object.</p>
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    1. COYou can assign 'null' to value-types when explicitly defined, e.g.: int? i; string s = "5"; i = s as int; // i is now 5 s = null; i = s as int; // i is now null
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    2. CORE: Anheledir Actually i would be null after the first call. You have to use an explicit conversion function to get the value of a string.
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    3. CORE: Sander Actually there is another very good reason to use as, it simplifies your checking code (Check for null rather then check for null and correct type) This is helpful since a lot of the time you would rather throw a custom one exception. But it is very true that blind as calls are bad.
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